World Interoperability for Microwave Access (WiMAX) is based on the IEEE 802.16 standard. Unlike IEEE 802.11a wireless LAN, the spread of which was delayed due to the problem of compatibility between equipment in different regions, the IEEE 802.16 standard was initially designed in consideration of compatibility with the European ETSI standard and thus has been recognized as a worldwide wireless MAN standard.
The IEEE 802.16 standard is divided into IEEE 802.16 in which Line-of-Sight (LOS) should be secured, IEEE 802.16a which uses low frequencies of 11 Ghz or less, and IEEE 802.16e to which restricted mobility and roaming functions have been added.
A full-duplex communication scheme is a scheme in which data can be simultaneously transmitted in both the uplink and downlink directions. A half-duplex communication scheme is a scheme in which data cannot be simultaneously transmitted in both the uplink and downlink directions although data can be transmitted in both the directions. That is, a half duplex terminal or Mobile Station (MS) performs only one of an operation for transmitting data or an operation for receiving data.
When the WiMAX system supports operation of a Frequency Division Duplex (FDD) MS within a Time Division Duplex (TDD) frame length of 5 ms, the length of each subframe has a length of equal to or less than 5 ms (for example, 5 ms, 2.5 ms, or 1.25 ms) and a preamble can be transmitted at intervals of 5 ms or less. Scheduling methods that can be used in this case include a method that takes into consideration a frame structure for each MS based on scheduling of the base station and a method which groups half duplex FDD MSs to create a frame based on the group.
FIG. 1 illustrates an example of a conventional full duplex FDD frame structure.
The frame structure of FIG. 1 causes no problem in the case of full duplex FDD operation. However, a downlink preamble 110 and a downlink MAP 120 collide with an uplink control region 130 in the case of half duplex FDD operation.
One method used to avoid such collision during half duplex FDD operation is to assign a DL/UL offset between a downlink frame and an uplink frame using an allocation start time or to group a downlink frame and an uplink frame.
However, even when this collision avoidance method is applied, it is not possible to reduce a transition time gap in the conventional frame structure or to prevent collision of a downlink preamble or control signal region with an uplink control channel and an excessive transition time occurs, hindering efficient utilization of resources during half duplex FDD operation.